1. Field of the Invention
The present invention relates to an LED (light emitting diode) driving circuit, and particularly relates to an LED driving circuit that is capable of activating the LEDs directly by an AC power supply, and the LEDs are arranged in a bridge circuit.
2. Description of Related Art
The LED is developed with advantages of low cost, low power dissipation, and high brightness, which are better than in other illumination devices.
The LED is driven by a DC voltage, so a voltage converter is required to transform an AC voltage to the DC voltage. A common LED driving circuit in prior art has a power supply, a bridge rectifier, a voltage detector and a current direction control circuit, wherein the bridge rectifier is connected to the power supply (AC power supply). The current direction control circuit consists of at least one current control unit, which is further coupled to the LEDs' cathode. The AC voltage is transformed into the DC voltage in the bridge rectifier, and the voltage detector will activate corresponding current direction control circuit based on the detected DC voltage level, to light an appropriate amount of LEDs, meanwhile, a filter capacitor is omitted.
Another example in U.S. Pat. No. 5,457,450 includes two rectifiers and two voltage compensation circuits.
The above examples both have a comparatively complex driving circuit; in addition, the heat dissipation is a problem in the complex circuit, which will further shorten the service life of the LEDs.
Therefore, the invention provides an LED driving circuit to mitigate or obviate the aforementioned problems.